1. Technical Field
The invention relates to a capacitor bank installation for generating reactive power in high or extra high voltage electrical power systems. In particular, the invention relates to such a capacitor bank installation on which capacitors are connected between a three phase high voltage power line and a three phase lower voltage power line replacing the heretofore high voltage shunt capacitor bank installations enabling less expensive switching devices to be utilized. The two voltage systems associated with the three phase high voltage and low voltage power lines are in phase.
2. Background Information
Shunt capacitor banks are normally used to generate reactive power in high or extra high voltage electrical power systems to maintain the normal voltage level during heavy loading conditions or system contingencies. Above 300kV, it is very difficult, if not impossible, to find a switching device with a voltage rating close to the system operating voltage to be able to switch ungrounded wye shunt capacitor banks. Shunt capacitor banks above 300kV are grounded wye installations which are easier to switch. The grounded wye operation of the high voltage shunt capacitor banks dictated by the limited capability of the switching devices, has negative effects upon the electrical power system and equipment performance.
Electrical power system and equipment problems associated with grounded wye shunt capacitor bank operations can be summarized as follows:
Increased zero sequence harmonic current circulation in the electrical power system which produce additional losses and may create magnetic interference with the telephone lines.
Introduction of high magnitude/high frequency inrush currents into the station ground grid during bank energization which may produce misoperation or failure of the sensitive electronic equipment.
Discharge of electric energy stored in the capacitor bank into close-in line-to-ground faults on the transmission lines which create additional I.sup.2 t duty on the line circuit breakers.
Introduction of ground current circulation during capacitor bank unbalance operation which may result in the false operation of some type of sensitive ground fault detection relays.
Prior art examples of shunt capacitor bank installations are shown in U.S. Pat. Nos. 2,933,652, 3,248,607 and 3,270,246. These and other prior art capacitor banks all are connected to ground or have a floating neutral. U.S. Pat. Nos. 3,943,435, 3,947,725 and 4,329,638 show various other electrical devices for use with usual shunt type capacitor bank installations.
These is no known capacitor bank installation of which I am aware which is connected between high and low voltage power lines for generating reactive power in the high voltage power system and for transferring reactive power to the high voltage electrical power system from the lower voltage electrical power system which is connected thereto.